Sucrase-isomaltase deficiency is a rare disorder usually manifested as diarrhea in infancy. The presentation of such a deficiency in adulthood is even more rare, particularly when the individual has no history of childhood diarrhea. After a literature search, the 59-yr-old patient we report is the oldest to have been identified with this condition. The difficulties encountered in diagnosis when such a case occurs at this age that have not previously been reported are highlighted.